In an ink jet head, a flexible wiring material for supplying the electricity to an actuator is superimposed on and bonded to the actuator, extended from over the actuator, and a drive circuit in an IC chip form for driving the actuator is mounted on the extended portion, as disclosed in JP-A-2005-161760. In the ink jet head, as wiring patterns formed on the flexible wiring material are wired finely and in a high concentration in order to provide a high resolution, as a result of which an electrical resistance in the wiring patterns becomes high, it being necessary to make a wiring pattern linking the circuit drive and the actuator as short as possible, the drive circuit is disposed in a position near the actuator on the flexible wiring material. The flexible wiring material generally has a plurality of wiring patterns distributed on a base material made of a resin, ends of the wiring patterns form connection portions, and on the actuator and a substrate on an opposite side having terminals corresponding to the connection portions, the terminals and the connection portions of the wiring patterns are bonded by a conductive connecting material such as a solder or a conductive adhesive.
Herein, as the flexible wiring material and the actuator and substrate on the opposite side are bonded by melting the solder by thermocompression or the like, a portion of the flexible wiring material superimposed on the actuator expands due to a heat, but a portion extended from the actuator does not expand as it is not heated, meaning that a distortion occurs in a whole of the flexible wiring material due to a difference in expansion between the two portions. Although the flexible wiring material is disposed passing through a narrow gap in an apparatus while being bent appropriately, at that time, in the event that the heretofore described kind of distortion occurs, it becomes difficult to bend it as desired and pass it through the narrow gap. Also, in the event, as heretofore described, that the drive circuit mounted on the flexible wiring material is positioned near the actuator, when bending the distorted flexible wiring material, there is a possibility of a large force being exerted on a connection portion of the wiring pattern and the drive circuit, or of the distortion reaching the connection portion and disconnecting the connection portion.
To date, as a way of combating a problem in which, in the event that the flexible wiring material and the opposing substrate have a differing heat expansion rate, an imperfect connection with the flexible wiring material is likely occur due to a discrepancy of the expansion, configurations described in JP-A-06-314866 and JP-A-2004-96005 have been considered.
For example, in JP-A-06-314866, a flexible substrate sandwiches the wiring patterns (a conductor pattern in JP-A-2005-161760) between two sheets of polyimide film and is bonded, and a window is formed in a leading edge of the wiring pattern. When a connection terminal of the wiring patterns and the wiring pattern of a glass substrate are connected by means of a soldering, it being possible for a heat stress on the glass substrate caused by the soldering to escape from the window, it is possible to reduce an effect thereof, increasing a reliability of a connection.
Also, in JP-A-2004-96005, a base material of a flexible substrate including a central portion supporting base material in a central portion of the wiring patterns (a conductive wiring in JP-A-06-314866), and a leading end base material in each leading end of the wiring patterns, a connection portion of the wiring patterns is exposed between the two base materials, in the central portion supporting base material, at least one slit is formed between the wiring patterns in a form penetrating from an end positioned on one connection portion side to an end positioned on the other connection portion side. For this reason, when bonding the central portion supporting base material and the leading end base material by thermocompression, even in the event that there is a difference in a heat expansion rate of the base materials, it is possible to reduce a shearing force occurring in the bonding portion.